Digital images are typically created, viewed, and manipulated using computers. Thus, judgments concerning the desired appearance of the digital images are made based on how the images appear when displayed on digital display devices. When the digital images are created and manipulated for a motion picture, the image data stored on the computer must be converted into film images for projection in a theater.
Digital film recorders are used to convert the digital images into images on photosensitive motion picture film. The conventional digital film recorders use a light source (e.g., a laser) to expose each frame of the film as necessary to produce the desired image in the frame. The film is then advanced to the next frame and the process is repeated. When a strip of film has been recorded, it is sent to a laboratory for development into a color negative and, later, a positive print.
To provide a high quality digital motion picture, it is desirable to have the appearance of the motion picture that is projected and viewed by a theater audience match the appearance contemplated by the producer. Thus, the color of each location on the exposed film should substantially match the color of the corresponding picture element (“pixel”) on the digital display device used by the producer to produce the image. That is, color accurate renditions of the digital film imagery are desired. Matching the calorimetric appearance of a digital film, however, is an intricate problem because the appearance is influenced by the film development processes, disparate projection technologies, and varying viewing environments.
Conventional approaches to producing color images on film that match the originally produced digital images include using a measurement-based solution. By characterizing the digital display device and film response, a visual correspondence can be computed between the film and the digital projection. However, simply relying on the photometrically “correct” solution does not typically yield satisfactory results because the solution ignores the perceptual impact of differing viewing environments.
One difficulty in producing a film image that corresponds visually to the original digital image produced and/or stored on a computer includes what is sometimes referred to as a “gamut mismatch”, which involves the inability of the film to reproduce all the colors reproducible on the digital display device. One conventional solution is to map the colors, which are outside the film's gamut, to the closest point on the surface of the film's gamut while maintaining the colors that are initially inside the gamut. This solution, however, results in abrupt color changes and produces banding artifacts in the final image.